WASHINGTON (CNN) -- Authorities indicted 100 Americans and Egyptians on Wednesday in the smashing of an international identity theft ring billed as one of the largest cybercrime cases ever.

In a speech on cybercrime in San Francisco, FBI Director Robert Mueller said more than 50 people had been arrested and others were being sought.

Fifty-three of those charged are U.S. citizens. Most of the suspects live in Southern California, but officials identified four from Nevada and seven from North Carolina.

There was no immediate word on the number of arrests among the 47 Egyptians charged in the case, but U.S. officials expressed optimism that all of the defendants in both countries would be taken into custody.

The operation targeted two banks and about 5,000 U.S. citizens, with losses totaling more than $2 million, officials said.

Members of the alleged hacking ring engaged in a sophisticated operation called "phishing" in which personal information is fraudulently collected through unwitting responses to phony e-mails that appear to be from legitimate institutions.

Assistant FBI Director Keith Bolcar said the sophistication of the cybercriminals discovered in "Operation Physh Phry" was "evolving and troubling."

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"Criminally savvy groups recruit here and abroad to pool tactics and skills necessary to commit organized theft with a common greed and shared willingness to victimize Americans," Bolcar said at a news conference in Los Angeles.

U.S. officials praised their Egyptian counterparts.

The scheme originated in Egypt, where hackers were able to compromise two banks through "phishing."

They then contacted U.S. co-conspirators who opened accounts through which the bank's funds could be deposited and withdrawn. Some of the ill-gotten proceeds were then wired to the hackers in Egypt.